Microwave stripline devices

ABSTRACT

There is disclosed microwave stripline devices wherein a pair of parallel striplike signal conductors electromagnetically coupled and in one plane and a planar field modifying element in another plane are disposed between a pair of spaced ground plane elements. In one variation, signal terminals are connected to each end of each signal conductor to provide a backward wave coupler. In another variation signal terminals are connected to one end of each signal conductor, respectively, and the other ends of each signal conductor are interconnected to provide a phase shifter.

nite States Patent 72 Inventor Carl w. Ger-st [56] References Cited Skaneatles, N .Y. UNITED STATES PATENTS [21] Appl. No. 835,693 2,860,308 11/1958 Bales 333/10 [221 Wed June 23,1969 2 951 21s 7/1960 Arditi 333/10 451 Patented Mar. 2 1971 l e 3,094,677 6/1963 Theriot 333/10 [73] Assignee gnaren Mllsrxowave, Incorpo 3,358,248 12/1967 Saad 333/10 racuse, y Primary Examiner-Herman Karl Saalbach Assistant ExaminerSaxfield Chatmon,J r. Attorney-Camil P. Spiecens ABSTRACT: There isdisclosed microwave stripline devices wherein a pair of parallel striplike signal conductors electromagnetically coupled and in one plane and a planar field [54] MICROWAVE T E DEVICES modifying element in another plane are disposed between a 3 Clams 7 Drawmg pair of spaced ground plane elements. In one-variation, signal [52] US. Cl 333/10, terminals are connected to each end of each signal conductor 333/84 to provide a backward wave coupler. In another variation [51] int. Cl 1101p 5/14 signal terminals are connected to one end of each signal con- [50] Field of Search 333/10, 84, ductor,- respectively, and the other ends of each signal conduc- 84 (M) tor are interconnected to provide a phase shifter.

PATENIEDMAR 21911 sum 1 or 2 "Mil/ I'll /Y// //1///////// INVENTOR.

Carl Gersr ATTORNEY MICROWAVE STRIPLINE DEVICES This invention pertains to microwave stripline devices and more particularly to such devices for use as couplers and phase shifters.

In the past few years there has been a demand for more compact couplers and phase shifters for incorporation in systems which process microwave signals. This demand has lead to the use of stripline techniques to realize the desired devices. With stripline techniques there are two signal conductors disposed between two parallel ground plane elements. The signal conductors are substantially parallel and electromagnetically coupled to each other. In order to obtain the desired properties of such devices, it is necessary to control the coupling between the signal conductors. When the required coupling is high the signal conductors must be close together. Because of this closeness several problems arise. First any slight variation in the spacing between the signal conductors presents a very great variation in the coupling. Second, the signal connections to the ends of the signal conductors themselves can act as signal conductors which in turn modify the coupling between the two signal conductors. Their influence on the coupling increases with the closeness of the signal conductors and can disturb the operating properties of the devices unless compensated for. Such compensation requires more difficult and complex designing and restricts design flexibility.

It is therefore a general object of the invention to provide improved microwave signal-processing devices such as couplers and phase shifters.

It is another object of the invention to provide such improved devices which utilize stripline techniques.

It is a further object of the invention to provide improved microwave stripline couplers and phase shifters which include electromagnetically coupled signal conductors wherein much tighter coupling can be obtained than is usually available for a given spacing of the signal conductors.

Briefly, the invention contemplates a microwave stripline device which includes first and second spaced and parallel ground plane elements. Between the ground plane elements is a planar field-modifying element which is parallel to the ground plane elements. Two electromagnetically coupled signal conductors are disposed between the field-modifying element and the same one of the ground plane elements. Signals are fed to and from the signal conductors by terminal means connected thereto.

Other objects the features and advantages of the invention will be apparent from the following detailed description when read with the accompanying drawing which shows microwave stripline devices in accordance with the invention.

In the drawing:

FIG. 1 shows a top plane view of a microwave stripline coupler;

FIG. 2 shows a cross section of the coupler taken along the line 2-2 of FIG. 1;

FIG. 3 shows a cross section of the coupler taken along the line 3-3 ofFIG.1;

FIG. 4 shows a cross section of the coupler taken along the line 4-4 of FIG. 1;

FIG. 5 is a top plane view of a microwave stripline phase shifter according to the invention;

FIG. 6 is a cross section of the phase shifter taken along the line 6-6 of FIG. 5; and

FIG. 7 is a cross section taken along the line 7-7 of FIG. 5.

FIGS. 1 to 4 show a backward wave coupler 10 having four ports shown ideally at l2, 14, 16, and 18. The ports can in practice be coaxial connectors. A signal applied to port 12 divides and exits from ports 14 and 16. The signals flowing from ports 14 and 16 are in phase quadrature. No signal flows from port 18. Coupler 10 is of the stripline-type having upper and lower ground plane elements 20 and 22. The ground plane elements can be a continuous layer or sheet of copper. Fixed to the inner surfaces of the ground plane elements 20 and 22 are sheets 24 and 26 of dielectric material such as fibre glass board. The boards can provide a substrate for the ground plane elements and do provides mechanical spacing. Disposed between the ground plane elements and parallel thereto is a planar field modifying element 28 of copper or other electrically conductive material. In a plane parallel to and between field-modifying element 28 and ground plane element 22 are a pair of parallel and spaced striplike signal conductors 30 and 32 of a given width which is a function of the desired line impedance. The striplike signal conductors are a quarter of an operating wavelength long with their respective ends opposite each other, i.e. end 30A of conductor 30 is opposite end 32A of conductor 32. It should be noted that field-modifying element 28 has a width that at least spans the conductors 30 and 32 and preferably extends beyond their remote edges as shown in FIG. 1. In addition the length and position of fieldmodifying element 28 is such that it terminates substantially at the ends of the conductors 30 and 32.

The end 30A of conductor 30 is connected, via a signal conductor 12A to port 12; and the end 308 of conductor 30 is connected, via a signal conductor 14A to port 14. Similarly ends 32A and 32B of conductor 32 are connected, via signal conductors 16A and 18A, to ports 16 and 18, respectively. The widths of these conductors are greater than the width of conductors 30 and 32 to provide the required matching impedances.

Preferably, conductors 12A, 30 and 14A are integral, as are conductors 16A, 32 and 18A, and are printed" on one side of a dielectric substrate 34. On the other side of substrate 34 is printed field-modifying element 28. Substrate 34 provides mechanical separation between and support for the conductors and the field-modifying element.

Electrically, the electromagnetic coupling between signal conductors 30 and 32 is a function of their spacing from each other. The closer the spacing the tighter the coupling. However, the field-modifying element 28 increases the coupling for any given mutual spacing of the conductors 30 and 32. By way of analogy this can be seen if the conductors 30 and 32 are considered as the plates of a capacitor. First assume that element 28 is absent. Then the capacitance is a function of the thickness of the edges and length of the conductors which gives the area of the plates and the spacing between the opposed edges of the conductors which gives the spacing between the plates. Since the edge thicknesses are small, the capacitance is small and the signal coupling small. When element 28 is present, conductor 30 and element 28 are the plates of a capacitor as are conductor 30 and element 28. Now there are two capacitors in series. The area of the plates of one of the capacitors is the product of the length and width of conductor 30, the area of the plates of the other capacitor is the product of the length and width of conductor 32. Since the width of the conductors is at least an order of magnitude greater than their thickness in a practical case, and since the thickness of substrate 34 is at least an order of magnitude less than the spacing between conductors 30 and 32, the capacitance in the second case, i.e. with element 28 present, is at least about two orders of magnitude greater. Hence, tighter coupling can be obtained even for wide separations of the conductors 30 and 32.

FIGS. 5, 6 and 7 show a microwave stripline phase shifter 100. Signals fed to port 114 exit from port 118 shifted degrees in phase. Sincemost of the elements of phase shifter are similar to coupler 10 of FIGS. 1 to 4 reference characters raised by 100 will be used for like components and only the differences will be cited. In particular, the only difference is that the device is a two port device with ports 12 and 16 absent. Consequently, there are no conductors comparable to conductors 12A and 16A of FIG. 1. Instead, end A of signal conductor 130 is connected, via conductor I13, to the end 132A of conductor 132. It should be noted that FIG. 2 can also be considered as a cross-sectional view taken along the line 2-2 of FIG. 5 provided 100 is added to each of the reference numerals of FIG. 2.

There has thus been shown an improved microwave stripline coupler and phase shifter which, by using a fieldmodifying element in close proximity to the usual signal conductors to alter the electromagnetic field generated by signals passing through the conductors, yields greater coupling for a given separation of the conductors.

lclaim:

l. A microwave stripline device comprising first and second outer ground plane elements, said ground plane elements being in spaced parallel relationship, first and second signal conductors disposed in a plane which is parallel to and between said ground plane elements, each signal conductors being substantially one-quarter of an operating wavelength long and having the same given width, said signal conductors being at least electromagnetically coupled to each other, first signal terminal means connected to one end of said first signal conductor, second signal terminal means connected to one end of said second signal conductor, each of said signal terminal means having a width greater than said given width, and

a planar field-modifying element disposed parallel to and between said first ground plane element and the plane of said signal conductors, said planar field-modifying element being a planar member of conductive material having a width sufficient to transversely span said first and second signal conductors and a length substantially equal to the length of said signal conductors.

2. The microwave stripline device of claim 1 further comprising third signal terminal means connected to the other end of said first signal conductor and fourth signal terminal means connected to the other end of said second signal conductor whereby said microwave stripline device is a backward wave coupler.

3. The microwave stripline device of claim 1 further comprising a further signal conductor conductively interconnecting the other ends of said first and second signal conductors whereby said microwave stripline device is a broadband phase shifter. 

1. A microwave stripline device comprising first and second outer ground plane elements, said ground plane elements being in spaced parallel relationship, first and second signal conductors disposed in a plane which is parallel to and between said ground plane elements, each signal conductors being substantially onequarter of an operating wavelength long and having the same given width, said signal conductors being at least electromagnetically coupled to each other, first signal terminal means connected to one end of said first signal conductor, second signal terminal means connected to one end of said second signal conductor, each of said signal terminal means having a width greater than said given width, and a planar field-modifying element disposed parallel to and between said first ground plane element and the plane of said signal conductors, said planar field-modifying element being a planar member of conductive material having a width sufficient to transversely span said first and second signal conductors and a length substantially equal to the length of said signal conductors.
 2. The microwave stripline device of claim 1 further comprising third signal terminal means connected to the other end of said first signal conductor and fourth signal terminal means connected to the other end of said second signal conductor whereby said microwave stripline device is a backward wave coupler.
 3. The microwave stripline device of claim 1 further comprising a further signal conductor conductively interconnecting the other ends of said first and second signal conductors whereby said microwave stripline device is a broadband phase shifter. 